The present invention relates generally to feed systems for beam scanning and dual mode circular antenna arrays, and more particularly to a power distribution scanning switch feed for such arrays.
Prior art techniques for feeding beam scanning and dual mode circular antenna arrays are relatively complex, difficult to fabricate and adjust, and costly. These techniques include the use of two Butler matrices, and the use of one such matrix fed by a one-to-eight (1:8) power divider and eight separate phase shifters.
Also, in NRL (National Research Laboratories) Report number 6696, a disclosure was made by E. Sheleg which employs a Butler matrix fed by a 1:n power divider, and the Stanford Research Institute also investigated a bi-conical horn which forms a rotatable cardioid pattern. However, the latter was restricted to a four-element Butler matrix.
Although there has been other discussions in the literature regarding the need for simplification of such circular antenna array feeding schemes, no actual implementation has been described to date in technical reports.
In contrast thereto, the disclosed invention employs a relatively simple and less complex scheme to provide the required feed for such circular antenna array. The invention utilizes an eight element Butler matrix or an equivalent matrix which produces equal amplitude outputs (coupled to the circular array) with varying progressive phase modes when any of its eight inputs is excited.
The m=0 and m=.+-.1 mode inputs to this matrix are coupled to a one-to-three (1:3) power distribution and phase variable network. The matrix and power distribution/phase variable network make up a composite switch which produces a symmetrical power distribution centered about the peak and decreasing to a minimum on either side of the peak, and its max/min amplitude ratio can be optimized by varying the 1:3 power divider outputs coupled to the matrix. This is made possible by the use of a conventional 1:3 power divider coupled to the aforementioned m=0 mode and two conventional phase shifters which feed the m=.+-.1 mode inputs to the matrix. The power distribution of the matrix outputs including the max/min positions can be scanned across the outputs by selectively setting appropriate phase states of the phase shifters at the m=.+-.1 inputs of the matrix.
Thus, it can be seen that this new technique simplifies the network configuration because the 1:8 power divider or matrix is replaced by a 1:3 power divider. This has obvious cost and other advantages, and also has improved electrical performance because the ohmic interconnection line losses will be lower with this new design. Further, with the simpler design of the present invention, the amplitude taper of a circular array can be optimized to effectively miximize radiation from the peak directed elements and minimize the radiation from the rear directed elements in order to suppress the backlobe intensity.